1. Field of the Invention
The present invention relates to the plotting of an instructed horizontal path for a moving body that has to go from one obligatory point of passage to another in accordance with constraints dictated by instructed values of turning radius, the instructed values of approach direction in terms of route or course to be maintained at the obligatory points of passage and the instructions for danger zone avoidance.
2. Discussion of the Invention
It can be applied especially but not exclusively to the real-time plotting, by the navigation system of an aircraft, of a path to be followed between two obligatory points of passage that is in keeping with the constraints of approach direction and turning radius at the obligatory points of passage and the constraints of danger zone avoidance. This result is sought so that an aircraft on mission has a constantly updated flight plan on board that can be exploited at any time during the mission by the aircraft flight management system to provide the pilot with navigation assistance and, if necessary, to direct an automatic piloting system.
Hitherto, there has been no known method, within the scope of the computing capacities of flight management systems in present-day aircraft, for generating a horizontal path that meets the constraints of approach direction and turning radius at obligatory points of passage and of danger zone avoidance.
The path to be followed is therefore computed by means located on the ground when the mission is being prepared and is introduced into the flight management system of the aircraft before departure on mission.
However, the pilot, during flight, may have to follow a new path for example subsequently to a change in mission or the appearance of a new danger zone on the initial path. He therefore must determine a new path and follow it.
Determining a new path in operational conditions is a difficult task for the pilot because he often has to choose between many possibilities. It is difficult for him to appreciate which of these possibilities is most appropriate for his mission, especially as he must always decide very quickly. Furthermore, when the new path chosen has not been taken into account during the preparation of the mission, the pilot lacks the elements on board with which to make the new path exploitable by the flight management system and is required to take back the flight controls.
To relieve the pilot of the piloting task even in unexpected situations, it has been proposed to equip an aircraft with an additional navigational assistance computer capable of proposing new paths to resolve the problem raised. However, equipment of this kind proves to be very costly and does not entirely meet the pilot""s requirements since there is a lengthy response time, often incompatible with the reaction time imposed on the aircraft pilot. Furthermore, the proposed paths are often unsuited to the problem raised. They lack precision and cannot always be exploited by the aircraft flight management system, since the pilot himself has to take command of the flight controls in following the instructions given to him on the proposed paths.
Furthermore, as soon as the evasion routes within a field of danger zones becomes slightly winding, the methods generally used to compute the evasion path in these navigational assistance computers become incapable of preparing a path that crosses this field of danger zones without penetrating one of these zones or again they become incapable of meeting the planned goal. Indeed, to be able to plot the evasion paths in real time, these methods generally simplify the problem to be resolved by likening the danger zones to circles circumscribed within the contours of the danger zones. The result thereof is that these zones have elongated shapes. The paths obtained circumvent these zones at great distances leading to evasion paths lengths that are excessive and therefore highly penalizing in terms of compliance with any precise timing of the mission and fuel autonomy. Consequently, paths of this kind may be incompatible with the mission goals of an aircraft. Furthermore, when the danger zones are very close to each other, this approximate modelling in disk form leads to overlapping zones, thus ruling out a solution of penetration of the danger zone field.
The present invention seeks to eliminate these drawbacks.
It is also aimed at facilitating an aircraft pilot""s task by relieving him of the navigation problems linked to an unexpected re-routing during a mission preparation and transferring them to the flight management system of the aircraft,
To this end, there is proposed a method for the generation of a horizontal path of danger zone avoidance between two obligatory points of passage that complies with constraints of approach direction and turning radius at the obligatory points of passage and constraints of the avoidance of danger zones demarcated by contours.
According to this invention, this method is characterized in that it comprises the following steps:
the modelling of the contours of each danger zone by a succession of segments demarcated by geographical points,
the determining of the characteristics of a first homing circle and second homing circle, passing through the initial point, that are tangential to the initial route and have a radius corresponding to that of the initial turn, these two circles having directional senses of travel that are in reverse to each other, determined by the directional sense of the initial route,
the determining of the characteristics of a first capture circle and second capture circle passing through the final point, that are tangential to the final route and have a radius corresponding to the final turn, these two circles having directional senses of travel that are in reverse to each other, determined by the directional sense of the final route,
the determining of the characteristics of the tangential routes common to the homing circles and to the contour of each danger zone, common to the capture circles and to the contour of each danger zone,
among the previously determined tangents, the selection of a tangent to one of the homing circles and of a route tangential to one of the capture circles so that these two tangents define a path skeleton connecting a homing circle to a capture circle without penetrating a danger zone,
the determining of an automatically controllable evasion path that lies on the previously defined path skeleton, and
the following by the aircraft of the path thus defined.
The invention thus uses relatively simple computations, which can therefore be performed by the computation means presently available on aircraft, to determine a path for the avoidance of danger zones to be avoided, this path being capable of being implemented without delay in a form that is directly exploitable by the flight management system for automatic piloting. Furthermore, since the danger zones are modelled by successions of segments, the evasion paths go as close as possible to the avoidance zones without however penetrating therein.
According to a particular feature of the invention, this method furthermore comprises the optimizing of the evasion path by the addition of an intermediate path segment between the selected routes tangential to the homing circle and to the capture circle.
According to another particular feature of the invention, if the determined evasion path has a length exceeding a certain threshold that is pre-determined in relation to the length of the initial paths without danger zones, then the method furthermore comprises the determining of a path that penetrates the interior of the field of danger zones without going through a danger zone.
When the configuration of the danger zones allows it, these arrangements produce paths that are even shorter than the previously computed evasion path.
According to another particular feature of the invention, circles of equiprobability of danger are centered on points demarcating the contour segments of the danger zones, the diameter of these circles corresponding to a fineness of gridding of the terrain, the tangents to the danger zones that are determined being tangential to these circles.
Advantageously, the invention furthermore comprises the prior selection of danger zones to be taken into account for the computation of an avoidance path, in selecting all the danger zones having points of definition on their contour located in a disk centered in the middle of the segment demarcated by the initial and final points and including these points.